J-10 Thread IV
- Thread starter Jeff Head
- Start date
You are mixing 'top' with 'sustained'. It is correct to say any decent missile can pull very high G's. But only for a very brief time.
J-10C has DSI which deliberately limits its top speed to less than Mach 2.0. This should tell you how much designers care for high speed.
When someone talks about top speed this, top speed that, one immediate thought crosses my mind about that author.
Not at all. I am simply stating there is a limit to a missile structural integrity and that integrity is much less than a solid piece of metal.
I'm utterly confused by your statement. What does a missile's G limit has to do with its top speed? Those 2 are entirely different measurement of performance.
The way I see it is a tradeoff. They probably want stealthier design and maybe DSI being lighter and much less maintenance intensive is a happy side effect. The cost most likely is the lower max speed.
Top speed is still useful, whether it is for launching BVR missile, avoiding enemy missile, etc. Otherwise why do fighters today standardize on Mach 2 as a rule of thumb? Might as well go subsonic only and save on fuel if max speed is not important.
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Not at all. I am simply stating that there is a limit to a missile's designed structural integrity and that integrity is much less than a solid piece of metal and that integrity will be compromised by extreme external conditions. Air density/flow and gravity all play their parts.
What the original author talked about is known as 'forward momentum'. Imagine you jog with a 2-pound weight in your hand at 5 mph. When you drop that weight, you can say for a fraction of a second, that weight was traveling at 5 mph also but that forward speed is unsustainable and the weight follows a ballistic course downward. Just like bullets. This is because the weight has no propulsive force to maintain its forward speed. How long and how much does the forward momentum a plane contribute to the missile's forward speed at the time of separation? Missiles are heavy and all that contribution is lost as soon as the missile makes its first course correction. That imparted momentum suddenly becomes drag and a penalty. Is that a good thing?
The DSI Mach 2 speed limit is a myth. Your inlet pressure recovery for a DSI is dependent on your bump geometry and its interactions with the rest of the inlet geometry. The entire inlet from bump to engine face is one entire fluidic system that needs to be analyzed as a whole. You can’t draw any meaningful conclusions about this stuff by cherry picking components. It’s possible the J-10’s DSI doesn’t limit it to below Mach 2.0. It’s possible it does. But a DSI in of itself doesn’t really tell you anything.
You’re forgetting that a bullet doesn’t just get “dropped”. It’s *fired* out of the barrel. It has additional momentum relative to the frame of reference of the plane it’s fired from.
As for a missile drop, the missile is dropped *below* the plane before its motor fires. It doesn’t take very long for the missile to fire its motor and by falling below the plane it’s no longer in the path of the plane’s travel.
Is that so? Thanks for the clarification. I did not know that.
How do you think missiles make course corrections? Please, show us how extra forward momentum is a penalty to missile performance.